In my experience, properly designed, constructed and maintained flat roofs aren't any more problematic than pitched roofs.  

Found out the hard way though usually best to always pull or get the proper Permits pulled.

They don't want to get in hot water by not complying with someone who will certainly document their claim file with such infractions.Just check references and proper licensing. 

I personally believe that having good partnerships can be a HUGE boost to any business when structured properly with the right people.

It's my experience if a tenant howls loud and long enough and they were reasonable good tenants, we would let items go that might be difficult to prove like switch plate, light bulbs, burner pans (surprised they're charging for that as they almost always have burn marks).One thing that stands out is they did not make the proper effort to repair the roof. 

The document can be found under "Tools" - "File Place" and a screenshot is below for ease of navigating to the proper document.

If its thru a realitor you have to go thru proper channels. make an offer that allows both inspection and financial outs. try to get them as long as possible- say 30-60 days minimum.Once you control the deal- you can do your due diligence to see if it really is a good deal.

If it is hung properly, it will last just as long as anything...metal has to be externally insulated too. 

the proper term might be wood floors. 

Along with that, you have liability issues that you can be exposed to if you don't properly hire, document, and pay contractors.